The present invention relates to computer animation. More specifically, the present invention relates to methods and apparatus for realistic grooming of simulating objects in computer animation.
In computer graphics imagery, motions and positions of secondary objects, such as hair, clothing, and plants are usually too complex for a human animator to directly control at every stage of a computer animation. Instead, animator specifies physical properties of the secondary or simulated objects for use by a computer program. The computer program then uses physically-based numerical methods and techniques to simulate the motions and positions of the secondary objects over time based on their physical properties.
For simulated clothing objects, the animator specifies the physical properties of the hair, such as how the hair bends due to forces or collisions with solid objects and how the hair deforms or collides with itself. The human animator also specifies spring or torsion forces that act on the hair that attempt to preserve the hair in the posed shape during simulation. The human animator may specify external forces acting on the hair, such as gravity and wind.
The animator also specifies motions and positions of kinematic or non-simulated objects (e.g., characters upon which the clothing objects rest). The animation of a non-simulated object is independent of and otherwise unaffected by motions and positions of simulated objects. However, the motions and positions of the non-simulated objects often principally influence motions and positions of simulated objects that are associated with the non-simulated object.
Consider a computer animation of a human character, having a hair style groomed by a human animator. The human character (i.e., the kinematic object) is directly animated by the skilled human animator. The hair of the human character is also posed or groomed to a desired shape and style. Then the computer program simulates motion of the hair (i.e., the simulated object) using physically-based numerical techniques.
However, problems exists with physically-based numerical methods and techniques used in computer animations where simulated objects (e.g., the primary characters of a scene) are posed in a particular shape. In the real world, hair usually sits on top of other hair that influences the shape and motion of the hair on top. If the physical properties and external forces acting on a simulated object are accurately modeled, the resulting motion of the simulated object will be plausible and seemingly realistic. However, it is too complex for a human animator to model every hair on the human head.
In our hair example, the animator models enough of the hair of the human character to achieve the desired hair groom. One problem is that the forces that hold the groom will prevent the hair from hanging down and moving naturally according to the motions of the non-simulated human character. This results in the hair remaining in the posed shape, and looking plastic or unrealistic.
Accordingly, what is desired are improved methods and apparatus for simulating physical properties of objects posed by an animator in a computer animation without the drawbacks discussed above.